Cygwin was fun. I'd done zero development on Windows, but about 10 years ago I had to figure out how to deploy some nightly shell scripts across a bunch of local computers in a few dozen offices, where about 80% were MacOS and the rest were Windows. I don't remember exactly how I rigged it, but basically cygwin allowed me to keep the scripts as they were and trigger them in place, with a few small modifications.

I never want to deal with that again ;)

[edit] fwiw, Termux on Android is similarly a fun pseudo-environment. It's a nice and helpful toy.